DESCRIPTION: The PTK family of receptors plays a central role in the development, differentiation and survival of neural cells. The overall objective of this research program is to understand the function of the ErbB Splice variants of NRG-1 have been shown to serve different functions and this application proposes to first identify NRG2 and NRG-3 variants as they may perform distinct roles. The second aim is to identify the sites of expression in the developing and mature nervous system. This analysis should permit the potential identification of a subset of signaling cells. Preliminary findings indicate that NRG-2 and NRG-1 have distinct activities and the third aim proposes to measure these activities in neural and cardiac cells. The distinct bioactivities of NRG-2 and NRG-3 suggest that other NRG and ErbB genes remain to be discovered and aim 5 initiates a search for novel homologs.